A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction.
An embodiment of the lithographic apparatus constructed to generate an extreme ultra violet (EUV) light is known from United States Patent Application Publication No. 2007/0012889. In the known apparatus in order to enrich the EUV beam propagating from an EUV source towards illumination system of the lithographic apparatus a gaseous spectral purity filter comprising ZrCl4 is provided. The spectral purity filter of the known lithographic apparatus may be located in a region that receives a beam of EUV-containing light from the EUV source and delivers the beam to a suitable downstream EUV optical system, wherein the beam from the source is arranged to pass through the spectral purity filter prior to entering the optical system. The ZrCl4 based gaseous spectral purity filter is configured to enrich the beam in at least one EUV wavelength as the beam passes through it.